February 5, 2013

Popular theories have placed the Neanderthal extinction at about 35,000 years ago, based on dating of the earliest bone fossils found at a Neanderthal site in southern Iberia. However, researchers from Australia and Europe are now refuting that evidence after taking another careful look at the bones and implementing an improved method to filter out contamination. Based on the new study, the Neanderthal may have actually died out much earlier, closer to 50,000 years ago.

This new theory shakes up the popular belief that has been held in place for some 20 years. It was a widely accepted fact Homo neanderthalensis persisted in southern Iberia while modern humans (homo sapiens) were advancing in the same region. But the international study, in which researchers from the Spanish National Distance Education University (UNED) participated, pokes holes in that hypothesis.

If the new evidence holds any weight, then the popular theory that modern humans and Neanderthals co-existed–and possibly even interbred–for millennia has just been shot down, especially as another hugely accepted theory shows modern humans didn´t settle in the region until 42,000 years ago.

The new study used the improved dating method “ultrafiltration,” a technique that removes modern carbon that can contaminate ancient collagen in bones. Using the new method, lead researcher Dr. Rachel Wood, of Australian National University (ANU), and her colleagues tested 215 bones from 11 sites where previous radiocarbon dating had supported the later survival of Neanderthals. The study is published today (Feb. 4) in the journal Proceedings of the National Academy of Sciences (PNAS).

The team found the vast majority of the bones contained insufficient collagen to be successfully dated. But of those that could be tested, Wood and her colleagues found enough evidence that placed the earliest record to be about 50,000 years ago at two separate sites.

Wood said the new evidence doesn´t completely exclude the possibility that Neanderthals lived until 35,000 years ago. Because radiocarbon testing couldn´t be accurately completed on many of the fossils, it´s possible some may have been from a later period. But for the two of the 11 sites examined, Wood says the evidence suggests Neanderthals died out 50,000 years ago.

"It is improbable that the last Neanderthals of central and southern Iberia would have persisted until such a late date, approximately 30,000 years ago, as we thought before the new dates appeared" assured coauthor JesÃºs F. JordÃ¡, researcher of the Department of Prehistory and Archaeology at UNED.

Wood and her team said the new dating method puts the extinction at closer to 50,000 years, but may be as late as 45,000 years ago, still much earlier than when modern humans started arriving in the region.

"The problem with radiocarbon dating alone is that it does not provide reliable dates older than 50,000 years" explained JordÃ¡. An additional problem is contamination; the older the samples are the more residues are accumulated. If contaminants are not removed the obtained dates are incorrect.

"The results of our study suggest that there are major problems with the dating of the last Neanderthals in modern-day Spain," said coauthor Thomas Higham, deputy director of the Radiocarbon Accelerator Unit at Oxford University in England. "It is unlikely that Neanderthals survived any later in this area than they did elsewhere in mainland Europe."

Chris Stringer, a senior research fellow at Britain´s Natural History Museum, said traditional dating techniques often lead to older radiocarbon dates, but as the technology improves, science has to follow suit. He added that the new technique now needs to be applied to other sites in Spain.

"Until this is done, there must be a significant question mark over the possible late survival of Neanderthals in the region," Stringer, who was not involved in the new study, told the Associated Press.

If other sites turn out to be older, then it is likely that encounters between Neanderthals and humans had to have taken place much earlier than previously believed, he added.

"Evidence from Britain, Belgium, France, Germany and Italy is increasingly pointing to a modern human presence before 40,000 years ago," said Stringer. "The new chronology suggests that any interaction between the last Neanderthals and the earliest moderns in Europe will similarly move before, rather than after, 40,000 years."

There is a chance that Neanderthals survived longer in other areas of Europe. "There are some other possible areas that may have also acted as a refuge for the species, such as the Caucasus, but the 'young' radiocarbon dates in these areas have also found to be problematic," Wood acknowledged.

Over the years scholars have been perplexed over disparities in the dates given to Neanderthal sites in north and south Iberia, and now the new evidence may explain why previous dating methods didn´t match up.

Higham, who believes there was some overlap between early man and Neanderthals, said further work would be needed to confirm the findings.

The new dating technique had applied the earlier extinction at the sites of Jarama VI and Zafarraya. Most of the other sites could not offer clear radiocarbon dating except for Cueva Anton (Murcia), which still provided recent dates in accordance with the popular theory that Neanderthals existed until 35,000 years ago. However, even at this site, the team said the remains are not clearly related to Neanderthals and more testing needs to occur.

In light of the new evidence, JordÃ¡ explained that "prehistory books would need revision", especially as new results become available. "Although it is still controversial to change the theory in force, the new concept, which presents new data indicating that Neanderthals and H. sapiens did not co-exist in Iberia, is becoming accepted" he added.